| 1. |
- Andresen, Louise C., 1974, et al.
(författare)
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Nitrogen dynamics after two years of elevated CO2 in phosphorus limited Eucalyptus woodland
- 2020
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 150, s. 297-312
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Tidskriftsartikel (refereegranskat)abstract
- It is uncertain how the predicted further rise of atmospheric carbon dioxide (CO2) concentration will affect plant nutrient availability in the future through indirect effects on the gross rates of nitrogen (N) mineralization (production of ammonium) and depolymerization (production of free amino acids) in soil. The response of soil nutrient availability to increasing atmospheric CO2 is particularly important for nutrient poor ecosystems. Within a FACE (Free-Air Carbon dioxide Enrichment) experiment in a native, nutrient poor Eucalyptus woodland (EucFACE) with low soil organic matter (≤ 3%), our results suggested there was no shortage of N. Despite this, microbial N use efficiency was high (c. 90%). The free amino acid (FAA) pool had a fast turnover time (4 h) compared to that of ammonium (NH4+) which was 11 h. Both NH4-N and FAA-N were important N pools; however, protein depolymerization rate was three times faster than gross N mineralization rates, indicating that organic N is directly important in the internal ecosystem N cycle. Hence, the depolymerization was the major provider of plant available N, while the gross N mineralization rate was the constraining factor for inorganic N. After two years of elevated CO2, no major effects on the pools and rates of the soil N cycle were found in spring (November) or at the end of summer (March). The limited response of N pools or N transformation rates to elevated CO2 suggest that N availability was not the limiting factor behind the lack of plant growth response to elevated CO2, previously observed at the site.
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| 2. |
- Andresen, Louise C., 1974, et al.
(författare)
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Patterns of free amino acids in tundra soils reflect mycorrhizal type, shrubification, and warming
- 2022
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Ingår i: Mycorrhiza. - : Springer Science and Business Media LLC. - 0940-6360 .- 1432-1890. ; 32:3-4, s. 305-313
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Tidskriftsartikel (refereegranskat)abstract
- The soil nitrogen (N) cycle in cold terrestrial ecosystems is slow and organically bound N is an important source of N for plants in these ecosystems. Many plant species can take up free amino acids from these infertile soils, either directly or indirectly via their mycorrhizal fungi. We hypothesized that plant community changes and local plant community differences will alter the soil free amino acid pool and composition; and that long-term warming could enhance this effect. To test this, we studied the composition of extractable free amino acids at five separate heath, meadow, and bog locations in subarctic and alpine Scandinavia, with long-term (13 to 24 years) warming manipulations. The plant communities all included a mixture of ecto-, ericoid-, and arbuscular mycorrhizal plant species. Vegetation dominated by grasses and forbs with arbuscular and non-mycorrhizal associations showed highest soil free amino acid content, distinguishing them from the sites dominated by shrubs with ecto- and ericoid-mycorrhizal associations. Warming increased shrub and decreased moss cover at two sites, and by using redundancy analysis, we found that altered soil free amino acid composition was related to this plant cover change. From this, we conclude that the mycorrhizal type is important in controlling soil N cycling and that expansion of shrubs with ectomycorrhiza (and to some extent ericoid mycorrhiza) can help retain N within the ecosystems by tightening the N cycle.
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| 3. |
- Bonaglia, Stefano, 1983, et al.
(författare)
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High methane emissions from an anoxic fjord driven by mixing and oxygenation : High methane emissions from fjords
- 2022
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Ingår i: Limnology and Oceanography Letters. - : Wiley. - 2378-2242. ; 7:5, s. 392-400
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Tidskriftsartikel (refereegranskat)abstract
- Oceanic methane (CH4) budgets lack data from high-latitude fjords that often behave as intermittently anoxic ecosystems with potentially high methane emissions. We conducted 15 expeditions and 49 in situ lander deployments in an anoxic Scandinavian fjord between 2009 and 2021. Benthic fluxes were highest at the deepest anoxic site (average 516μmol CH4 m−2 d−1), supporting bottom water methane exceeding 5000nM. Natural and engineered mixing events displaced methane-rich bottom waters, enhancing upper water concentrations and driving high sea–air flux reaching 641μmol CH4 m−2 d−1. Mixing also reduced pelagic methane oxidation from 70% to 20% of all methane sources into the fjord. Upscaling of literature fluxes combined with our results suggests that fjords globally emit 1.0±0.8 Tg CH4 yr−1. Despite their small global area, fjords are hotspots of methane release. We suggest that ongoing deoxygenation and global change will enhance methane emissions from fjords.
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| 4. |
- Fernández-Fernández, María, et al.
(författare)
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Fire severity and post-fire mulching effects on N transformation rates of temperate soils during the first critical winter–spring period
- 2022
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Ingår i: European Journal of Soil Science. - : Wiley. - 1351-0754 .- 1365-2389. ; 73:5
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Tidskriftsartikel (refereegranskat)abstract
- Wildfires are increasing worldwide and, therefore, the extents of their on- and off-site impacts are particularly important on soil erosion and nutrient cycles. To mitigate post-fire erosion, mulching is increasingly being used, but its effects on the nitrogen (N) cycle are poorly known. To fill this gap of knowledge, gross N fluxes were modelled with Ntrace to compare with unburnt soils (US) the effects of intermediate (BI) and high severity (BH) burning, and post-fire straw mulching (BIM and BHM). Two wildfires, two-time points after the fire and 20 soil-treatment combinations were studied. The mineralization of soil organic N to NH4+ (MSON) increased in BI (1.9–6.9×) with respect to US, with no clear trends observed in BH and mulched treatments. In most soils, NH4+ immobilisation in labile ((Formula presented.)) and recalcitrant soil organic matter (SOM) ((Formula presented.)) was more important than abiotic NH4+ fixation ((Formula presented.)) and together were larger (3.5–11×) in BI than in US, while contrasting results were found depending on time after a fire (BH, BHM, BIM) and wildfire characteristics (BHM, BIM). Autotrophic nitrification ((Formula presented.)) was included in the best model for all soils, whereas heterotrophic nitrification (OSON) was undetectable in most BH soils. Total nitrification ((Formula presented.) + OSON) decreased with time after the fire in BH, increased in US and BI, and was differently affected by mulching depending on fire severity and time from the fire. While NO3− immobilisation ((Formula presented.)) was frequently modelled only for BI soils, the dissimilatory NO3− reduction to NH4+ (DNRA) was retained in the best models for all soils and it was reduced by soil burning, whereas a short-lived increase was induced by mulching. Denitrification ((Formula presented.)), modelled for most soils, was negatively affected by burning and positively by mulching. In summary, wildfires tended to increase MSON and (Formula presented.), decrease DNRA and (Formula presented.) and had no clear influence on (Formula presented.) and nitrification. These effects are usually mitigated by mulching which, however, tended to enhance nitrification. Highlights: Direction and magnitude of changes in soil gross N fluxes depend on fire severity. Usually, wildfires increased MSON and (Formula presented.), and decreased DNRA and (Formula presented.). No clear post-fire trend was found for (Formula presented.) and nitrification. Fire effects on gross N fluxes are (partially) counterbalanced by mulching.
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| 5. |
- Gil, J., et al.
(författare)
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Sources of nitrous oxide and the fate of mineral nitrogen in subarctic permafrost peat soils
- 2022
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 19:10, s. 2683-2698
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Tidskriftsartikel (refereegranskat)abstract
- Nitrous oxide (N2O) emissions from permafrost-affected terrestrial ecosystems have received little attention, largely because they have been thought to be negligible. Recent studies, however, have shown that there are habitats in the subarctic tundra emitting N2O at high rates, such as bare peat (BP) surfaces on permafrost peatlands. Nevertheless, the processes behind N2O production in these high-emission habitats are poorly understood. In this study, we established an in situ N-15-labeling experiment with two main objectives: (1) to partition the microbial sources of N2O emitted from BP surfaces on permafrost peatlands and (2) to study the fate of ammonium and nitrate in these soils and in adjacent vegetated peat (VP) surfaces showing low N2O emissions. Our results confirm the hypothesis that denitrification is mostly responsible for the high N2O emissions from BR. During the study period, denitrification contributed similar to 79 % of the total N2O emissions from BP, whereas the contribution from ammonia oxidation was less (about 19 %). Both gross N mineralization and gross nitrification rates were higher in BP than in VP, with high C/N ratios and a low water content likely limiting N transformation processes and, consequently, N2O production in the latter soil type. Our results show that multiple factors contribute to high N2O production in BP surfaces on permafrost peatlands, with the most important factors being the absence of plants, an intermediate to high water content and a low C/N ratio, which all affect the mineral-N availability for soil microbes, including those producing N2O. The process understanding produced here is important for the development of process models that can be used to evaluate future permafrost-N feedbacks to the climate system.
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| 6. |
- Håkansson, Charlotta, 1971-
(författare)
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Greenhouse Gas Fluxes and Carbon Sequestration in Young Norway Spruce Stands : The Effects of Fertilization
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The enormous challenge of climate change is discussed and debated today because of its major impact on life on Earth. The forests have an important role to play as the plants absorb carbon dioxide (CO2) from the atmosphere through their photosynthesis and the growing tree retain carbon (C). Hence, the larger the growth the greater the carbon storage and climate benefit. The demand for wood and wood products is increasing as well as the ongoing debate about forest management. Therefore, alternative management methods to increase wood production is of interest and the effects these methods could have on climate change mitigation. In this context this Thesis deals with the effect of fertilization on carbon balance and growth in young forest as well as flows of the greenhouse gases, CO2, methane (CH4), and nitrous oxide (N2O) from forest land. In addition, it deals also with the reliability and comparability of different measurement methods which are compared with respect to the carbon balance.The studies have been carried out in a young mixed stand of Norway spruce (Picea abies (L.) Karst) and birch (Betula pendula and B.pubescens) on a storm-felled (Gudrun 2005) area in southern Sweden, Kronoberg county. Part of the area was fertilized with 150 kg N ha-1 everysecond year from 2014 and forward, while the other part was kept unfertilized. In the unfertilized part a dose experiment was set up where 0,150, 300, and 450 kg N ha-1 were added to investigate the impact of the different fertilizer levels on forest floor greenhouse gas fluxes. Chamber measurements of forest floor fluxes, eddy-flux measurements of stand net-fluxes and tree measurements of height, diameter and birch leaf biomass were conducted in different, occasionally overlapping, periods in the years 2013-2021.The results show that even if the flows of CO2 from the forest floor increase initially after a first standard fertilization, the effect decreases quickly. The net fluxes show that the stands become carbon sinks already eight years after the storm with a net uptake of about 18 ton CO2 ha-1 yr-1 of. The forest floor fluxes of CH4 and N2O also show a short-term effect of fertilization, however the levels are very low compared to CO2. The fertilization induced increase of total tree biomass growth increased with time. The results show that 12 and 15 years after regeneration, the fertilization compared to the control has increased the tree growth by 3.4 and 6.3 m3 ha-1 yr-1 and carbon storage by 4.7 and 8.7 ton C ha-1 yr-1 respectively.Comparison of measurement results of the Eddy-flux technique's netflows and chamber measurements of soil respiration together with tree growth shows the importance of calibrating the measurement methods when the results are later to be used in modeling future climate scenarios.
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| 7. |
- Ibáñez, T. S., et al.
(författare)
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Mid-term effects of wildfire and salvage logging on gross and net soil nitrogen transformation rates in a Swedish boreal forest
- 2022
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127 .- 1872-7042. ; 517
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Tidskriftsartikel (refereegranskat)abstract
- Wildfires are natural and important disturbances of boreal forest ecosystems, and they are expected to increase in parts of the boreal zone through climate warming. There is a broad understanding of the immediate effects of fire on soil nitrogen (N) transformation rates, but less is known about these effects several years after fire. In July 2014, a large wildfire in the boreal forest zone of Central Sweden took place. Four years after the wildfire, we measured processes linked to the soil N cycle using the 15N pool dilution method (for gross N mineralization, consumption and nitrification) and the buried bags method (for net N mineralization), in soils from stands of different fire severity that had or had not been subjected to salvage logging. Gross N mineralization and consumption rates per unit carbon (C) increased by 81 % and 85 % respectively, in response to high fire severity, and nitrification rates per unit C basis decreased by 69 % in response to high fire severity, while net N mineralization was unresponsive. There was no difference in the effect of salvage logging across stands of differing fire severity on N transformation rates, although concentrations of resin adsorbed nitrate (NO3–) were overall 50 % lower in logged compared to unlogged stands. We also found that irrespective of burn severity, N immobilization rates exceeded N nitrification rates, and immobilization was therefore the dominant pathway of gross N consumption. Gross N consumption rates were higher in burned than unburned stands, despite there being a higher active microbial biomass in unburned soil, which suggests an even higher immobilization of N over time as the microbial biomass recovers following fire. Our study shows that soil N transformation rates were more affected by changes in fire severity than by salvage logging, and that four years after the fire many aspects of the N cycle did not differ between burned and unburned stands, suggesting substantial resilience of the N cycle to fire and salvage logging. However, we note that long term impact and many additional ecosystem properties or processes should be evaluated before concluding that salvage logging has no ecosystem impact. Furthermore, shortened fire regimes following climate warming accompanied with shorter intervals between salvage logging practices, could still impact the capability for the N cycle to recover after an intense fire. While wildfire in the boreal region results in a shift from nutrient conserving to nutrient demanding plant species, our results suggest this shift is dependent on a relatively short-lived pulse of higher N cycling processes that would have likely dissipated within a few years after the fire.
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| 8. |
- Kononets, Mikhail Y, 1978, et al.
(författare)
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In situ incubations with the Gothenburg benthic chamber landers : Applications and quality control
- 2021
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 214
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Tidskriftsartikel (refereegranskat)abstract
- In situ incubations of sediment with overlying water provide valuable and consistent information about benthic fluxes and processes at the sediment-water interface. In this paper, we describe our experiences and a variety of applications from the last 14 years and 308 deployments with the Gothenburg benthic chamber lander systems. We give examples of how we use sensor measurements for chamber leakage control, in situ chamber volume determination, control of syringe sampling times, sediment resuspension and stirring quality. We present examples of incubation data for in situ measurements of benthic fluxes of oxygen, dissolved inorganic carbon, nutrients, metals and gases made with our chamber landers, as well as manipulative injection experiments to study nitrogen cycling (injections of N-15 nitrate), phosphate retention (injections of marl suspension) and targeted sediment resuspension. Our main goal is to demonstrate the possibilities that benthic chamber lander systems offer to measure solute fluxes and study processes at the sediment-water interface. Based on our experience, we recommend procedures to be used in order to obtain high quality data with benthic chamber landers.
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| 9. |
- Lammirato, C., et al.
(författare)
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Measuring frequency and accuracy of annual nitrous oxide emission estimates
- 2021
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923. ; 310
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Tidskriftsartikel (refereegranskat)abstract
- Accurate estimates of cumulative N2O fluxes from agricultural soil are essential for quantifying global N2O emissions and for identifying effective mitigation strategies. This study focuses on the short term temporal variability of N2O fluxes, and on how the accuracy of annual cumulative estimates is affected by different (simulated) measuring frequencies of an automatic system based on the closed chamber method. Fluxes were measured with high temporal resolution (24 per day) for approximately one year on agricultural soil in the southwest of Sweden. The short-term temporal variability of N2O fluxes was considerable: the predictive power of measured fluxes decreased to negligible levels in a time frame of 4-5 h, and large intraday flux ranges were observed frequently, particularly in days with soil temperatures below 0 degrees C. A time of day well suited for consistently providing good estimates of the mean daily flux could not be identified. Consequently, the accuracy of annual emission estimates strongly depended on the measuring frequency. Multiple measurements per day were necessary for consistently quantifying annual emission estimates with accuracy. Accuracy improved with measuring frequency increasing up to four times per day, and higher frequencies generated negligible further improvements. Based on this study the following recommendations are made with regard to measuring frequency: i) measure four times per day for maximum accuracy and ii) measure twice per day for a good compromise between accuracy and the number of plots that can be monitored.
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| 10. |
- Makelele, I. A., et al.
(författare)
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Conservative N cycling despite high atmospheric deposition in early successional African tropical lowland forests
- 2022
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 477, s. 743-758
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Tidskriftsartikel (refereegranskat)abstract
- Background Across the tropics, the share of secondary versus primary forests is strongly increasing. The high rate of biomass accumulation during this secondary succession relies on the availability of essential nutrients, such as nitrogen (N). Nitrogen primarily limits many young secondary forests in the tropics. However, recent studies have shown that forests of the Congo basin are subject to high inputs of atmospheric N deposition, potentially alleviating this N limitation in early succession. Methods To address this hypothesis, we assessed the N status along a successional gradient of secondary forests in the Congo basin. In a set-up of 18 plots implemented along six successional stages, we quantified year-round N deposition, N leaching, N2O emission and the N flux of litterfall and fine root assimilation. Additionally, we determined the N content and C:N stoichiometry for canopy leaves, fine roots, and litter, as well as delta N-15 of canopy leaves. Results We confirmed that these forests receive high amounts of atmospheric N deposition, with an increasing deposition as forest succession proceeds. Additionally, we noted lower C:N ratios, and higher N leaching losses, N2O emission, and foliar delta N-15 in older secondary forest (60 years). In contrast, higher foliar, litter and root C:N ratios, and lower foliar delta N-15, N leaching, and N2O emission in young (< 20 years) secondary forest were observed. Conclusions Altogether, we show that despite high N deposition, this early forest succession still shows conservative N cycling characteristics, which are likely indicating N limitation early on in secondary forest succession. As secondary succession advances, the N cycle gradually becomes more open.
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